I just did that exact same upgrade this week, i had the 3600+ running at 3ghz and now i have the 5000+ which is running at 3.26ghz. Might be able to squeeze a little more out of it but i need to play with different multiplier combos still.
If you're looking for a good cooler for cheap I got the AC freezer 64. Great little guy and is keeping my oc going nice and cool.
As for RAM, NCIX had 2GB of Crucial ballistix for $14.99 yesterday but they sold out at that price and at $19.99 as well.
you should wait for a bit, see if you x2 3600+ clocks well, by waiting for a bit buy getting RAM and the CPU Cooler, then when you get more cash, pick up the 5000+ BE
my 5000 clocks approximately 3-400mhz higher than my 3600 would. not a tremendous difference, but higher in any event. it does higher clocks (than the 3600) on stock voltage if you choose to overclock it in that fashion (ie raising the multiplier instead of the external clock).
You should wait for a bit, see if you x2 3600+ clocks well, by waiting for a bit buy getting RAM and the CPU Cooler, then when you get more cash, pick up the 5000+ BE